1. Field of the Invention
The present invention relates to a semiconducting ceramic and an electronic element a fabricated from the ceramic. More particularly, the present invention relates to a semiconducting ceramic having a positive temperature characteristic and an electronic element fabricated from the same.
2. Background Art
Conventionally, semiconducting electronic elements having a positive temperature coefficient of resistance (hereinafter referred to as a PTC characteristic)--meaning that electrical resistance increases drastically when temperature exceeds Curie temperature--have been used to protect a circuit from overcurrent or to demagnetize elements of a color television set. In view of their advantageous PTC characteristic, semiconducting ceramics predominantly comprising barium titanate have generally been used in such semiconducting electronic elements.
However, in order to make barium-titanate based ceramics semiconducting, firing must generally be performed at a temperature of 1300.degree. C. or more. Such treatment at high temperature has the following drawbacks: a tendency to damage the furnace used for firing; high cost of maintaining the furnace; and high energy consumption. Thus, there has been demand for semiconducting ceramics comprising barium titanate which can be fired at a lower temperature.
To overcome the above drawbacks, a modified technique is disclosed in "Semiconducting Barium Titanate Ceramics Prepared by Boron-Conducting Liquid-Phase Sintering" (In-Chyuan Ho, Communications of the American Ceramic Society, Vol. 77, No. 3, p829-p832, 1994). Briefly, the temperature at which the ceramics exhibit semiconduction is lowered by addition of boron nitride to the barium titanate. The literature reports that the boron nitride-added ceramics can become semiconducting at a firing temperature of about 1100.degree. C. Although the temperature at which conventional ceramics exhibit semiconduction has decreased, the temperature is still more than 1000.degree. C. and the decrease is still unsatisfactory.